Brief(ish) background...
I'm late 20s, married, me and DH have careers we are progressing in and are not exactly well-off but comfortable enough for the two of us.
I have DS and DB a few years younger than me. DS has toddler, works PT, lives with her non-working partner and they're skint all the time. DB is the youngest, and although academically clever enough, messed about in school, failed GCSEs and has done nothing since leaving school (6 years ago).
Our parents divorced just before I did my GCSEs but I'd already come to terms with the fact they were going to separate and it never really affected me, however both parents changed a LOT after divorce, something I only really realised in the past couple of years.
DS and DB were 9 & 10 at divorce, lived with DM and visited DF at weekends for the first couple of years.
When DB got into his teens he started causing trouble at school, DF found weed in his room, got arrested for petty stuff with his friends etc, and started a cycle of moving between DF and DM every few months. In the meantime, DF got re-married and DM was having very loud, angry, on-again, off-again rship with another man who moved in and out of our house, and he seems to have been her sole priority, even over us. I went off to uni and when I was home for hols was always working, so maybe this is why none of this made sense until recently...
Anyway, about 2 years ago my DB had a breakdown, left a suicide note (but didn't actually do it..) and then was admitted for mental health problems, had social workers etc etc. This was hugely traumatic and for a while we couldn't leave him on his own, DM took a lot of time off work etc, but after a while it regressed again - he stopped going to his appointments, went back to substance abuse, sleeping all day, waking in the early hours, disappearing overnight, etc. He was living with DM at this time, but would sporadically move into his on/off GF family home, who also substance abuse etc, so no good for him to be around, and each time they got back together he'd cut all contact with us, sometimes would go two or three months with no contact at all.
Moving back and forward between DM and DF and both getting more and more annoyed with his lack of, well... anything. DF enrolled him onto various courses/volunteer things and either wouldn't start them or quit almost immediately. No chance of paid employment as no experience.
Fast forward to early 2013, announces his on/off GF is pregnant. Think this will change his attitude somehow, but it doesn't.
DF enrols him on course, tells him that this is his last chance, if he doesn't stick with it then the next time his GF kicks him out, he'll have to go to the council and get emergency housing/shelter to live at as he's had enough. Quits course, moves in with GF, GF kicks him out. DM refuses to let him move back with her as he's 'making her ill'. DS has no room/money to keep him.
Which leaves me and DH. He could sleep on our sofa, we don't have a spare bed or anything, but this has caused arguments between DH and I - why should we go out to work to pay our rent etc to keep DB, a grown man, who has had chance after chance to sort his life out? Is being cruel to be kind better? Why is it our responsibility? DM/DF should be taking some responsibility for their son. DH is usually the most easy going person in the world, we have a fantastic relationship, but he's said that if DB ends up living with us, he'll have serious problems with my DM/DF. I can't stop thinking about this, I feel like the worst person in the world, I feel responsible and guilty even though I know it isn't my place, but it's also making it difficult for me to have a relationship with my parents, as I feel it's their fault he's 'turned out like this' and they should fix it.
I don't know what to do, I feel like I want to run away from them all...